1. Field of the Invention
The present invention relates to a liquid crystal display (LCD) apparatus, and more particularly, to the alignment of a flexible printed board with a printed wiring board.
2. Description of the Related Art
Generally, an LCD apparatus is constructed by an LCD panel, at least one flexible printed board and a printed wiring board. The flexible printed board drives the LCD panel and has leads or input terminals. The printed wiring board has leads or connection pads to be connected the input terminals of the flexible printed board.
In a first prior art LCD apparatus, alignment holes are perforated in the flexible printed board, and alignment holes are perforated in the printed board. When the flexible printed board is mounted on the printed wiring board, the alignment holes of the flexible printed board are in alignment with the corresponding alignment holes of the printed wiring board, i.e., one of the alignment holes of the flexible printed board is superposed onto one of the alignment holes of the printed wiring board. In this case, the alignment holes are used only for alignment, not for reinforcing the mounting of the flexible printed board on the printed wiring board. This will be explained later in detail.
In the first prior art LCD apparatus however, since the alignment holes of the flexible printed board are perforated independent of the leads thereof, and the alignment holes of the printed wiring board are perforated independent of the leads thereof, a relative displacement error of the alignment holes of the flexible printed board and a relative displacement error of the alignment holes of the printed wiring board are superposed onto each other to create a large error of alignment.
In addition, after the flexible printed board is mounted on the printed wiring board, bending stress is applied to the leads of the flexible printed board, so that disconnections and cracks are generated in these leads.
In a second prior art LCD apparatus (see: JP-A-5-21515), an LCD panel is mounted on a glass substrate. Also, input terminals or electrodes are formed on the glass substrate and are electrically connected to the LCD panel. Also, dummy electrodes for alignment are formed on both sides of the series of electrodes. The width of some of the dummy electrodes is half of that of the electrodes, and the width of the other dummy electrodes is twice of that of the electrodes. This will also be explained later in detail.
In the second prior art LCD apparatus, an alignment along one direction is precisely carried out; however, an alignment along the other direction is impossible.
In a third prior art LCD apparatus (see: JP-A-5-346562), T-shaped alignment marks are formed on a first transparent substrate, and reversed-T-shaped alignment marks are formed on a second transparent substrate. In this case, the spacing between the alignment marks deviates stepwise at a prescribed size, so that the two kinds of alignment marks form slide calipers. Therefore, the first transparent substrate can be precisely in alignment with the second transparent substrate. This will also be explained later in detail.
In the third prior art LCD apparatus, however, the number of alignment marks required to form the slide calipers is large, so that a large space therefor is required. Thus, the alignment system of the third prior art LCD apparatus cannot be applied to the alignment of a flexible printed board to a printed wiring board.
In a fourth prior art LCD apparatus (see: JP-A-6-51331) fixed patterns are provided on both sides of the flexible printed board, and fixed pads are provided on the printed wiring board to correspond to the fixed patterns. The fixed patterns are soldered to the fixed pads, thus reinforcing the coupling of the flexible printed board to the printed wiring board. This will also be explained later in detail.
In the fourth prior art LCD apparatus, however, the fixed patterns and the fixed pads do not serve as alignment markers, and therefore, such alignment markers need to be provided which increases the occupied space of the flexible printed boards and the spacing therebetween.
In a fifth prior art LCD apparatus (see: JP-A-3-289628), flexible printed boards are in alignment with a printed wiring board by penetrating spacer elements therethrough, which are made of plastic or like. Then, the upper and lower portions of the spacer elements are caulked so that the flexible printed board are fixed to the printed wiring board. This will also be explained later in detail.
In the fifth prior art LCD apparatus, however, the operations for penetrating and fixing the spacer elements require time, thus increasing the manufacturing cost.